1. Introduction to Flowcharting
A Supplement to Starting Out with C++, 4th Edition by Tony Gaddis Published by Addison-Wesley

2. What is a Flowchart?
START
Display message “How many hours did you work?”
Read Hours
Display message “How much do you get paid per hour?”
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
Display Gross Pay
END
A flowchart is a diagram that depicts the “flow” of a program.
The figure shown here is a flowchart for the pay-calculating program in Chapter 1.

3. Basic Flowchart Symbols
Rounded Rectangle
START
Display message “How many hours did you work?”
Read Hours
Notice there are three types of symbols in this flowchart:
rounded rectangles
parallelograms
a rectangle
Each symbol represents a different type of operation.
Display message “How much do you get paid per hour?”
Parallelogram
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
Rectangle
Display Gross Pay
Rounded Rectangle
END

4. Basic Flowchart Symbols
Terminal
START
Display message “How many hours did you work?”
Terminals
represented by rounded rectangles
indicate a starting or ending point
Read Hours
Display message “How much do you get paid per hour?”
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
START
Display Gross Pay
END
Terminal
END

5. Basic Flowchart Symbols
START
Display message “How many hours did you work?”
Input/Output Operations
represented by parallelograms
indicate an input or output operation
Read Hours
Display message “How much do you get paid per hour?”
Input/Output Operation
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
Display message “How many hours did you work?”
Read Hours
Display Gross Pay
END

6. Basic Flowchart Symbols
START
Display message “How many hours did you work?”
Processes
represented by rectangles
indicates a process such as a mathematical computation or variable assignment
Read Hours
Display message “How much do you get paid per hour?”
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
Process
Multiply Hours by Pay Rate. Store result in Gross Pay.
Display Gross Pay
END

7. Stepping Through the Flowchart
START
Output Operation
Display message “How many hours did you work?”
Read Hours
How many hours did you work?
Display message “How much do you get paid per hour?”
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
Variable Contents: Hours: ? Pay Rate: ? Gross Pay: ?
Display Gross Pay
END

8. Stepping Through the Flowchart
START
Display message “How many hours did you work?”
Read Hours
Input Operation
(User types 40)
How many hours did you work? 40
Display message “How much do you get paid per hour?”
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
Variable Contents: Hours: 40 Pay Rate: ? Gross Pay: ?
Display Gross Pay
END

9. Stepping Through the Flowchart
START
Display message “How many hours did you work?”
Read Hours
How much do you get paid per hour?
Display message “How much do you get paid per hour?”
Output Operation
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
Variable Contents: Hours: 40 Pay Rate: ? Gross Pay: ?
Display Gross Pay
END

10. Stepping Through the Flowchart
START
Display message “How many hours did you work?”
Read Hours
How much do you get paid per hour? 20
Display message “How much do you get paid per hour?”
Read Pay Rate
Input Operation
(User types 20)
Multiply Hours by Pay Rate. Store result in Gross Pay.
Variable Contents: Hours: 40 Pay Rate: 20 Gross Pay: ?
Display Gross Pay
END

11. Stepping Through the Flowchart
START
Display message “How many hours did you work?”
Read Hours
How much do you get paid per hour?
Display message “How much do you get paid per hour?”
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
Process: The product of 40 times 20 is stored in Gross Pay
Variable Contents: Hours: 40 Pay Rate: 20 Gross Pay: 800
Display Gross Pay
END

12. Stepping Through the Flowchart
START
Display message “How many hours did you work?”
Read Hours
Your gross pay is 800
Display message “How much do you get paid per hour?”
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
Variable Contents: Hours: 40 Pay Rate: 20 Gross Pay: 800
Output Operation
Display Gross Pay
END

13. Four Flowchart Structures
Sequence
Decision
Repetition
Case

14. Sequence Structure a series of actions are performed in sequence
The pay-calculating example was a sequence flowchart.

15. Decision Structure
One of two possible actions is taken, depending on a condition.

16. Decision Structure
A new symbol, the diamond, indicates a yes/no question. If the answer to the question is yes, the flow follows one path. If the answer is no, the flow follows another path
YES NO

17. Decision Structure
In the flowchart segment below, the question “is x < y?” is asked. If the answer is no, then process A is performed. If the answer is yes, then process B is performed.
YES NO
x < y?
Process B
Process A

18. Decision Structure
The flowchart segment below shows how a decision structure is expressed in C++ as an if/else statement.
Flowchart
C++ Code
YES NO
x < y?
Calculate a as x times 2.
Calculate a as x plus y.
if (x < y)
a = x * 2;
else
a = x + y;

19. Decision Structure
The flowchart segment below shows a decision structure with only one action to perform. It is expressed as an if statement in C++ code.
Flowchart
C++ Code
YES NO
x < y?
Calculate a as x times 2.
if (x < y)
a = x * 2;

20. Repetition Structure
A repetition structure represents part of the program that repeats. This type of structure is commonly known as a loop.

21. Repetition Structure
Notice the use of the diamond symbol. A loop tests a condition, and if the condition exists, it performs an action. Then it tests the condition again. If the condition still exists, the action is repeated. This continues until the condition no longer exists.

22. Repetition Structure
In the flowchart segment, the question “is x < y?” is asked. If the answer is yes, then Process A is performed. The question “is x < y?” is asked again. Process A is repeated as long as x is less than y. When x is no longer less than y, the repetition stops and the structure is exited.
x < y?
Process A
YES

23. Repetition Structure
The flowchart segment below shows a repetition structure expressed in C++ as a while loop.
Flowchart
C++ Code
x < y?
Add 1 to x
YES
while (x < y)
x++;

24. Controlling a Repetition Structure
The action performed by a repetition structure must eventually cause the loop to terminate. Otherwise, an infinite loop is created.
In this flowchart segment, x is never changed. Once the loop starts, it will never end.
QUESTION: How can this flowchart be modified so it is no longer an infinite loop?
x < y?
Display x
YES

25. Controlling a Repetition Structure
ANSWER: By adding an action within the repetition that changes the value of x.
x < y?
Display x
Add 1 to x
YES

26. A Pre-Test Repetition Structure
This type of structure is known as a pre-test repetition structure. The condition is tested BEFORE any actions are performed.
x < y?
Display x
Add 1 to x
YES

27. A Pre-Test Repetition Structure
In a pre-test repetition structure, if the condition does not exist, the loop will never begin.
x < y?
Display x
Add 1 to x
YES

28. A Post-Test Repetition Structure
This flowchart segment shows a post-test repetition structure.
The condition is tested AFTER the actions are performed.
A post-test repetition structure always performs its actions at least once.
Display x
Add 1 to x
YES
x < y?

29. A Post-Test Repetition Structure
The flowchart segment below shows a post-test repetition structure expressed in C++ as a do-while loop.
Display x
Add 1 to x
YES
x < y?
C++ Code
do { cout << x << endl; x++; } while (x < y);
Flowchart

30. Case Structure
One of several possible actions is taken, depending on the contents of a variable.

31. Case Structure
The structure below indicates actions to perform depending on the value in years_employed.
CASE years_employed 1 2 3
Other
bonus = 100
bonus = 200
bonus = 400
bonus = 800

32. Case Structure 1 2 3 Other If years_employed = 2, bonus is set to 200
CASE years_employed 1 2 3
Other
bonus = 100
bonus = 200
bonus = 400
bonus = 800
If years_employed = 1, bonus is set to 100
If years_employed is any other value, bonus is set to 800

33. Connectors Sometimes a flowchart will not fit on one page.
A connector (represented by a small circle) allows you to connect two flowchart segments. A

34. Connectors
The “A” connector indicates that the second flowchart segment begins where the first segment ends. A
START
END

35. Modules
A program module (such as a function in C++) is represented by a special symbol.

36. Call calc_pay function.
Modules
START
END
Read Input.
Call calc_pay function.
Display results.
The position of the module symbol indicates the point the module is executed.
A separate flowchart can be constructed for the module.

37. Combining Structures
Structures are commonly combined to create more complex algorithms.
The flowchart segment below combines a decision structure with a sequence structure.
x < y?
Display x
Add 1 to x
YES

38. Combining Structures
This flowchart segment shows two decision structures combined.
Display “x is within limits.”
Display “x is outside the limits.”
YES NO
x > min?
x < max?

39. Review What do each of the following symbols represent?
(Answer on next slide)

40. Answer What do each of the following symbols represent? Decision
Terminal
Input/Output Operation
Connector
Process
Module

41. Review
Name the four flowchart structures.
(Answer on next slide)

42. Answer
Sequence
Decision
Repetition
Case

43. Review
What type of structure is this?
(Answer on next slide)

44. Answer
Repetition

45. Review
What type of structure is this?
(Answer on next slide)

46. Answer
Sequence

47. Review
What type of structure is this?
(Answer on next slide)

48. Answer
Case

49. Review
What type of structure is this?
(Answer on next slide)

50. Answer
Decision